Which of the following is a symptom of hyperparathyroidism?

Hyperparathyroidism is primarily characterized by an increased secretion of parathyroid hormone (PTH), which leads to elevated levels of calcium in the blood, a condition known as hypercalcemia. One of the common symptoms associated with this elevation of calcium is the development of kidney stones. The excess calcium can lead to the formation of calcium stones within the kidneys, which may cause symptoms such as pain and hematuria (blood in urine).

This condition's effect on the kidneys, combined with the alterations in mineral metabolism, plays a critical role in understanding why kidney stones are a prominent symptom. The other options, such as low calcium levels, decreased appetite, and increased muscle mass, do not align with what is typically observed in hyperparathyroidism, as the primary endocrine imbalance does not support these symptoms. Instead, they contrast with the expected clinical picture of elevated calcium levels and associated complications.